Chi Zhang, Pei Wang, Zhouyu Chen, Binbin Zhai, Xiangquan Liu, Helan Zhang, Junxia Peng, Yinan He, Haonan Peng, and Yu Fang, ACS Applied Materials & Interfaces 2025, DOI: 10.1021/acsami.4c22309.

Polymer materials, with their advantages of light weight, high strength, and corrosion resistance, are widely used in manufacturing, agriculture, transportation, and electronic appliances. However, polymers are highly flammable, with a low ignition point, prone to rapid ignition and the release of harmful gases, posing significant safety hazards. Therefore, enhancing the flame retardancy of polymers is of paramount importance. Current primary flame-retardant strategies include physical blending, chemical crosslinking, and surface coating methods. However, these approaches face issues such as environmental pollution, high costs, and vulnerable coatings, necessitating the development of novel eco-friendly flame-retardant strategies. Water, as a low-cost, environmentally friendly, and non-flammable substance, offers great potential for developing innovative flame-retardant polymers. Using the emulsion-templating method, water can be uniformly dispersed in a polymer matrix at the micro-to-nano scale, forming solid-liquid composite materials. This method, through the regulation of pore structures and balancing the Marangoni effect and Ostwald ripening effect, effectively enhances the flame retardancy of the material, providing a promising pathway for developing eco-friendly polymer materials.

Figure 1. The appearance changes and thermal resistance performance of cPSs-M2 in combustion tests.

Figure 2. The flame retardant properties and performance comparison of cPSs-M2.

In this study, we pioneered the use of water as a flame retardant, successfully preparing solid-liquid composite materials based on crosslinked polystyrene foam (cPSs) using the emulsion-templating method. These materials exhibit a fully enclosed pore structure. In UL-94 testing, the solid-liquid composites demonstrated exceptional flame-retardant performance, achieving a flame resistance rating of V-0. The peak heat release rate (PHRR) and total heat release (THR) were significantly reduced, while the ignition time (TTI) and flame performance index (FPI) were increased by more than 10 times and 25 times, respectively. By applying a micrometer-thick hydrophobic coating to the material surface and using saltwater instead of pure water, we achieved flame-retardant durability exceeding eight years. Unlike traditional flame-retardant strategies, this study integrates water as a flame retardant into the material interior, leveraging water's high specific heat and heat of vaporization to achieve green and efficient flame retardancy through cooling, dilution, and smothering effects. This research not only lays the foundation for the development of revolutionary, novel eco-friendly flame-retardant materials but also demonstrates tremendous commercial potential and broad prospects in practical applications.

First Author: Zhang Chi, master’s student, Shaanxi Normal University

Correspondence Authors: Prof. Fang Yu, Prof. Peng Haonan, Ms. He Yinan, Shaanxi Normal University

Full Text Link: https://doi.org/10.1021/acsami.4c22309